European Patent Application Publication No. 0 467 673 A2, published on Jan. 22, 1992 describes and discusses a method and apparatus for actively counteracting a disturbing force acting horizontally on an elevator platform moving vertically in a hoistway. Therein the horizontal acceleration of the ear is sensed and counteracted, for example, by means of an active roller guide, meaning a conventional roller guide with one or more actuators added thereto. In one embodiment thereof, a roller guide was fitted with two actuators, one for heavy-duty centering and the other for countering high frequency accelerations with much lesser forces. A slower, position-based feedback control loop was disclosed for controlling the high-force, centering actuator. Position and acceleration sensors were disclosed as being positioned at various points in the system, including the floor or roof, but the positions thereof were explicitly indicated as being arbitrary, see page 10, line 33.
In U.S. Pat. No. 5,027,925 there is shown and described a procedure and apparatus for dampening the vibrations of an elevator car. As discussed therein, the elevator is provided with an elastic suspension system and an accelerometer that provides signals to control a counteracting force. The elevator is provided with high pass filters to filter out signal components relating to the elevator's normal travelling acceleration.
One obvious way of implementing such a closed-loop acceleration based control system is to place the accelerometers close to their associated actuators. For an active roller guide system, this suggests mounting the accelerometers on the roller guides themselves.
It is clear from the prior art that the presence of high frequency horizontal accelerations, or vibrations, is a major obstacle that must be overcome in order to provide an improved ride quality. As used in the art, the phrase "high frequency" is generally taken to mean mechanical vibrations having a frequency greater than about 10 Hz. Such high frequency accelerations make the implementation of control loops quite difficult since control loop stabilization is significantly affected by many spurious responses occurring beyond about 20 Hz. Thus, the prior art has addressed this problem with considerable vigor and expense. Unfortunately, the solutions were not feasible because of the inability to remove spurious responses using conventional linear lumped parameter filters.
Consequently, it is necessary to provide an active vibration control system that overcomes the difficulties of the prior art systems.